The present invention is directed to a clamping mechanism for an impulse sealer and more particularly to an improved hand-operated lever system adapted to more quickly clamp the article and more efficiently exert a higher degree of pressure on the article subsequent to clamping.
Heat sealing machines currently used for forming and sealing bags of thermoplastic material are generally catagorized into two types, namely a heated element type and an impulse type. The former type employs a heat sealing method which is carried out by pressing an object to be sealed against a constantly heated element. This type is suitable for mass-production purposes involving certain materials because of the short period of heating time required thereby but is unsuitable for processing other materials which are not capable of withstanding the high temperature of the heating element such as cellophane-laminated polyethylene film. On the other hand, the latter type involves the pressing of a thermoplastic film to be sealed against a band-like electric heating wire which is protected by a layer of non-adhesive material such as a TEFLON-coated glass fiber cloth. The heating wire may be electrically heated in a very short period of time thereby allowing the use of not only ordinary thermoplastic film, but also laminated ones which may be subjected to pressures and temperatures over a wide range. As a result, this method is widely used for small or medium scale processes but requires a positive clamping of the object to be sealed. In order to obtain the force for clamping the object properly, treadle, solenoid and air cylinder means have been widely used. On the other hand, manually operated lever types have also been used to a large extent for simplifying the operation. Many of these hand operated types depend on a lever system operated by one hand so that the object to be sealed must be held in the proper position by the other hand. With such an arrangement, the clamping of the object is difficult, especially when the contents of the bag to be sealed are relatively large.
In order to overcome this problem, hand operated sealing mechanisms have been devised wherein the work table for supporting the article to be sealed is also adapted to act as the driving arm to initiate the clamping function when depressed. An example of such a conventional hand operated sealer is shown in FIG. 1, wherein the driving arm B which also supports the article to be sealed is pivotally supported at one end by a stationary fulcrum A. A sealing bar C is pivotally connected to the mid-point of the arm B by means of a pivot F. One end of the sealing bar C is connected to a suitable support through a spring S and the opposite end of the sealing bar C is provided with a clamping head H which is adapted to engage the support bed D on the arm B for clamping materials to be sealed. The sealing bar C is also connected between the spring S and the pivot F to a roller G which is rotatable about a fixed pivot so that upon lowering of the arm B, the sealing bar C will pivot downwardly to bring the clamping head H into engagement with the support bed D. In this system, assuming the distance between fulcrum A and depression point E to be (L.sub.1), the distance between the fulcrum A and the pivot F to be (L.sub.2), the distance between the center of the roller G and the pivot F to be (l.sub.1) and the distance between the center of the roller G and the pressure head H to be (l.sub.2), the force P' exerted by the pressure head on the bed is related to the force P at the depression point E as (l.sub.1 /l.sub.2) is related to (L.sub.1 /L.sub.2) and since (l.sub.1) is far smaller than (l.sub.2), the total compressive force P' is considerably weaker than P since L.sub.1 is designed to be longer than L.sub.2. Therefore, as a practial matter, it is very difficult to generate sealing pressure sufficient to obtain satisfactory sealing using a hand operated sealer of this type.